Flat bed image scanner

ABSTRACT

A flat bed image scanner uses a contact image sensor to scan a document. The distance between the contact image sensor and the glass window, over which the document is placed, is minimized and held constant by inserting a lubricating element between the contact image sensor and the glass window. The lubricating element may comprise two pads placed at the two ends of the contact image sensor. The lubricating element can also be integrated structurally with the contact image sensor. The material of the lubricating element can be nylon or some other kinds of plastic. The lubricating element may also comprise two guide rails placed at the two edges of the scan window.

This is a continuation-in-part patent application of U.S. patent application Ser. No. 08/705,170, filed Aug. 29, 1996 now U.S. Pat. No. 5,801,851.

BACKGROUND OF THE INVENTION

This invention relates to image scanners for providing document and picture information to computers, in particular to flat bad image scanners.

A flat bed image scanner is widely used today is a periphery equipment for scanning documents, books and pictures and for furnishing the scanned information to a computer to be processed. However, traditional flat bed image scanner leaves much to be desired in terms of cost and volume. In other words, it is desirable to develop a smaller and less costly flat bed image scanner.

FIG. 1 shows the structure of a conventional flat bad image scanner, which includes an image reading sensor 11 c, a glass window 5, a sliding guide 7, a frame 12, driving mechanism (not shown) and image processing circuit (not shown). The principle of operation is as follows:

A document or picture 13 is placed over a window 5. The image 6 is irradiated with a light source 11 a which is mounted on an optical carriage 11. The reflected light L passes through a group of reflecting mirrors 111, 112, 113 and lens 11 b, and impinges on an image sensor 11 c. Signals sensed by the sensor 11 c are processed by electronic circuits (not shown) to be digitized. After the sensor 11 c completes scanning the signals from one row or one area, a translating mechanism (not shown) moves the carriage 11 along the guide 7 to a next scanning position. The carriage 11 is held in place by a flange 11 d which wraps around the guide 7. This scanning continues until complete image information is read.

The biggest drawback of such a carriage 11 containing the light source 11 a, the reflecting mirrors 111, 112, 113, the sensors 11 c and the flange 11 d, lies in its bulkiness and the long light path between the image appearing at position 6 and the reflected image appearing at the sensor 11 c. Take a standard size A4 paper, the distance between position 6 and the sensor 11 c is more than 26 cm. In a conventional “flat bed image scanner” with three reflecting mirrors, the optical carriage has a cross-sectional area of approximately 9 cm×6 cm.

It is desirable to reduce the size, the power consumption and the cost of a flat bed image scanner. One approach to overcome the problem is to forego the mirror and lens system as the basic element and use a “Contact Image Sensor” CIS to construct a flat bed image scanner. The flat bed image scanner can achieve small size. The contact image sensor used in the present invention as shown in FIG. 2 measures only 2 cm×2 cm approximately, containing a light source 1 a, a focusing lens 1 b, an image sensor 1 c, a dust shielding window 1 d, and a frame 1 e. Position 6 a is where an object is scanned. However, the contact image sensor has a drawback in that the depth of focus is very short, only 0.3 mm in depth. In other words, if position 6 a is off by 0.3 mm upwards or downwards, the image becomes fuzzy. On the other hand, the traditional optical system 11 shown in FIG. 1 has a depth of focus as deep as 5 mm.

Thus, it is necessary to overcome the problem of shallow depth of focus for a flat bed image scanner. The traditional optical system shown in FIG. 1 cannot be used directly for a contact image sensor, because when a contact image sensor rides on a track to travel, it is difficult to maintain an error of less than 0.3 mm between the object and the contact image sensor. Any fluctuation in mechanical dimension or change in temperature can cause deformation in material and renders mass production difficult.

SUMMARY

An object of this invention is to devise a structure adapted to the shallow depth of focus of a contact image sensor for use in a flat bed image scanner. Another object of this invention is to reduce the optical path in a flat bed image scanner. Still another object of this invention is to reduce the cross-sectional area of a flat bed image scanner.

These objects are achieved in this invention by using a novel structure for the contact image sensor. The contact image sensor is pressed against the glass window by a spring, so that the sensor can slide in intimate contact with the glass window. Thus, the distance between the scanned object and the contact image sensor can be held within an error 0.3 mm. Any error in mechanical precision or due to temperature fluctuation cannot adversely affect the scanning quality of the image scanner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of a conventional flat bad image scanner.

FIG. 2 shows the cross-section of a contact image sensor used in the present invention.

FIG. 3 shows the reading head of the present invention.

FIG. 4 shows the different components parts of the reading head.

FIG. 5A shows another embodiment of the present intention showing the side rail of a guide rail; FIG. 5B shows the bottom view of the window.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows the structure of the optical reading mechanism for the contact image sensor based on the present invention. A contact image sensor 1 is recessed in a nest 2. An elastic element 4 is used to push the contact image sensor 1 intimately against a glass window 5 a. This elastic element 4 can be spiral spring or a leave-shaped spring such as a C-shaped spring or S-shaped spring. A lubricating element 3 a, 3 b is inserted between the contact image sensor 1 and the glass window 5 a to reduce friction so that the contact image sensor can intimately glide along the surface of the glass window 5 a. The lubricating element is composed of material with low coefficient of friction, such as nylon or certain engineering plastic material. Such lubricating element 3 a, 3 b can also be integrated with the frame of the contact image sensor.

The sliding action between the contact image sensor 1 and the glass window 5 a can also be obtained by installing rollers at the two ends of the contact image sensor 5 a instead of using the lubricating media 3 a, 3 b.

The bottom of the nest 2 is attached to sliding sleeve 21. This sliding sleeve is mounted over a track 7 a, so that the nest can slide along the track 7 a and function to scan any document 13 a placed above the window 5 a.

FIG. 4 shows the individual component parts of the contact image sensor based on one embodiment of this invention. The two lubricating elements 3 a and 3 b are each placed at two respective ends of the contact image sensor 1. An elastic element 4 is inserted between the contact image sensor 1 and the nest 2, such that the contact image sensor is in intimate contact with one side of the window 5 a. The bottom of the nest of 2 is attached to a sleeve 21, which can slide along the track 7 a to function as a scanner.

FIGS. 5A and 5B show the cross-sectional view and the bottom view of another embodiment respectively Two lubricating guide rails 52 a and 52 b of low coefficient of friction are glued on the bottom side of the scan window 5 a. The image sensor 1 shown in FIG. 4 is guided to scan along two lubricating guide rails 52 a, 52 b, instead of using the lubricating element 3 a, 3 b.

The foregoing description illustrates only few embodiments of a flat bed scanner based on the present invention, the invention is not limited to these particular structures. Any other structures using the spirit and principle of placing the contact image sensor in intimate contact with the document window are all within the scope of this invention. 

What is claimed is:
 1. A flat bed image scanner for scanning a document to obtain data for digital processing, comprising: a glass window for placing said document; a contact image sensor for scanning said document; at least two lubricating guide rails placed between said contact image sensor and said glass window to reduce friction and to reduce fluctuation in mechanical dimension between said contact image sensor and said glass window when said contact image sensor slides along said glass window; a nest for recessing said contact image sensor; an elastic element placed in said nest for pushing said contact image sensor against said window; and a sliding mechanism for sliding said nest so that contact image sensor can scan said document.
 2. A flat bed image scanner as described in claim 1, wherein two of said lubricating guide rails are each placed at two respective edges of said contact image scanner.
 3. A flat bed image scanner as described in claim 2, wherein said lubricating guide rails are glued on said window.
 4. A flat bed image scanner as described in claim 1, wherein said lubricating guide rails are integrated with said window.
 5. A flat bed image scanner as described in claim 1, wherein the lubricating guide rails comprises durable plastic material. 